July 16, 2012 -- Getting a recommended seven hours of
sleep a night may help women keep their memory sharp, suggests a new analysis of data from the Nurses' Health Study.

The study found that women who slept five hours or less on average per day had lower scores on standard memory tests than those who slept seven hours, reports Elizabeth Devore, ScD, of Brigham and Women's Hospital in Boston.

Similarly, women who slept nine or more hours on average per night had lower memory scores than those who slept seven hours a night, Devore tells WebMD.

"Women who got too little or too much sleep had the memories of women about two years [their senior]," she says.

The link between sleep duration and memory held true both in mid-life and later life, Devore says.

The findings were presented in Vancouver at the Alzheimer's Association International Conference.

Many Don't Get Enough Sleep

A recent CDC study found that more than 40 million workers get less than six hours of sleep per night.

Devore notes that growing evidence suggests that getting more or less than the recommended seven hours per day of sleep is associated with an increased risk of heart disease and
type 2 diabetes.

"Since both heart disease and diabetes have been linked to an increased probability of having [memory] problems, we hypothesized that sleep duration may also influence memory," she says.

So the researchers examined data for more than 15,000 participants in the Nurses' Health Study. The women answered questions about how many hours they slept a night both in 1986 (when they were aged 40 to 65) and in 2000 (when they were aged 54 to 79).

Then, between 1995 and 2000, when the women were aged 70 or older, they took a series of memory tests. Follow-up memory tests were conducted every other year for six years.

"Interestingly, women whose sleep changed by two or more hours per day on average from mid- to later life had worse memory than those with no change in sleep duration, independent of their initial sleep duration," Devore says.

Dean M. Hartley, PhD, director of science initiatives at the Alzheimer's Association, points out that the study doesn't show cause and effect, only that there is an association between sleep and memory.

But other studies support a link, too. For example, researchers at Beth Israel Deaconess Medical Center found that a good night's sleep triggers changes in the brain that help to improve memory.

"We've had inklings of a link. And this is a very dynamic study with a large number of participants. Together with its other health benefits, including its role in protecting against heart disease and diabetes, this is yet another reason to get a good night's sleep," Hartley says.

Devore says she's hopeful that the work could eventually lead to new strategies to protect against impairment of memory and thinking abilities and also Alzheimer's disease.

Researchers are also trying to figure out whether sleep affects brain chemicals that may protect against dementia.

Sleep Tips

Some tips for a good night's sleep from the National Sleep Foundation:

Maintain a regular bed and wake time schedule, including weekends.

Establish a regular, relaxing bedtime routine such as soaking in a hot bath or hot tub and then reading a book or listening to soothing music.

These findings were presented at a medical conference. They should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.